The present invention relates to integrated circuit packages, and more particularly to a method of protecting the integrated circuit package from static electricity during the assembly process.
In the last few decades, the electronics industry has literally transformed the world. Electronic devices are used by, or affect the daily lives of, a large segment of the world's population. For example, telephones, television, radios, Personal Computers (PCs), laptop PCs, palmtop PCs, PCs with built-in portable phones, cellular phones, wireless phones, pagers, modems, and video camcorders, are just a few of the electronic products that have been developed in recent years and which have been made smaller and more compact, while providing more and/or enhanced functions than ever before. The integrated circuit (IC) chip, and the more efficient packaging of the IC chip, have played a key role in the success of these devices.
One of the most serious dangers to the electronics is static. In the electronic fabrication areas, static is controlled primarily to prevent the attraction of particles to the wafer surface. But the greatest concern is electrostatic discharge, or ESD. Static charge can build up to levels of tens of thousands of volts. If this voltage is suddenly discharged onto an IC chip surface, it can easily destroy all or a portion of the integrated circuit.
The integrated circuit (IC) device with its IC chip and embedded circuitry are delicate, and must be protected. Particularly, the IC device is susceptible to damage from static electricity. From the manufacturing processes through use of the IC device, special precautions are taken to prevent static electricity charges from contacting the IC chip and damaging it.
These precautions may include the operators use of grounding straps and nonstatic smocks; the use of antistatic carrier material; moving by lifting rather than sliding; and grounding equipment, work surfaces and floor mats.
The current method of dissipating static charge is by blowing ionized air onto the package at various stages of the assembly process. However, in some areas of the assembly and in some equipment, it is not possible to blow ionized air onto the package. Also, the amount of static charge removed by ionized air is difficult to measure.
Plastic packages are particularly susceptible to static charges that collect on the package surface during the manufacturing process. In most packages, all the metal leads, traces and contacts are connected to each other and to the ground of the device. The ground of the device is then regularly connected to an electrical ground in the equipment to dissipate any charge that collects in the device or package.
In some packages, the traces need to be separated after manufacturing and before the chip is attached to allow for the testing of the package and to remove defects. In these type of packages, that are no means of dissipating any of the static charges that may accumulate in the package. For example, in the process of manufacturing the IC substrate for plastic ball grid array (PBGA) packages, shorts and opens in the traces are present and need to be sorted and removed. This is done to avoid mounting a good device chip on a defective package. The plating busses are usually isolated from the traces for this purpose. However, these isolated traces in the package can collect static electricity during assembly of the package and when the chip is mounted and connected to the package, the chip can be damaged by this static electricity.
In view of the above, it is evident that what is needed is a means of providing an electrical connection to ground within the package during the assembly process in order to prevent static electricity from accumulating, and at the same time allow for testing of the package IC substrate and the device after assembly.